Low-Carb Diet and Diarrhea

Meg Campbell

About the Author:

Meg Campbell

Meg Campbell is a wellness expert with nearly two decades of experience as a fitness coach, group exercise instructor, and nutrition specialist. She began her full-time freelance writing career in 2010, and writes extensively about nutrition, health, and medicine. Ms. Campbell divides her time between the United States and Argentina.

Eating a high-fat diet can lead to diarrhea.
(Image: itakdalee/iStock/Getty Images)

Making a major change in your diet in an effort to lose weight or improve your health takes dedication and hard work. But learning the ins and outs of a new diet isn’t always the most challenging aspect of committing yourself to a different eating regimen. Sometimes, a change in diet can come with unwanted -- often gastrointestinal -- side effects. Experiencing persistent diarrhea after switching to a low-carb diet may just be temporary, or it may mean that you need to make some adjustments.

Major Change in Diet

Your body is used to the diet you’ve been feeding it, so a significant change in dietary composition can result in digestive distress. This isn’t necessarily linked to the type of change you’ve made – substantially boosting your fiber intake, going low-fat or shifting to a very-high-protein diet can all have the same kind of effect. Gastrointestinal symptoms include excess gas, abdominal discomfort, constipation and diarrhea. If your diarrhea is related to a major change in diet, it should gradually disappear as your body adjusts. Change-induced symptoms typically last anywhere from several days to a couple of weeks, depending on how readily your body adapts.

Temporary Fat Malabsorption

Because most low-carb diets strictly limit carbohydrates, a higher proportion of calories must come from fat and protein. Fat typically accounts for roughly 45 to 65 percent of calories in a low-carb diet. If your previous diet was relatively low in fat -- maybe the generally recommended 20 to 35 percent of calories -- your body probably hasn’t ever had to process a consistently high-fat diet. When your pancreas isn't producing enough fat-digesting enzymes to keep up with demand, improperly digested fat can cause diarrhea. Unless you have an underlying health problem, however, the condition is probably temporary and should be improved by consuming less fat.

But how much fat should you be consuming? While there’s no specific percentage that’s just right for everyone, you may want to try scaling back if you’re getting far more than 35 percent of your daily calories from fat. If your symptoms improve but don’t disappear, you may need to drop your fat intake even further. Keeping a food diary can help you find the intake ratio that’s right for your body.

Carbohydrate Malabsorption

Milk, sour cream, heavy cream, cheese and yogurt all contain varying levels of lactose, or milk sugar. If your transition to a low-carb diet included a significant boost in your intake of dairy products, your diarrhea may simply be a sign of lactose intolerance. If that’s the case, reducing your dairy intake, or removing more problematic products from your diet, may be the key. Hard cheeses, for example, contain far less lactose -- and fewer carbohydrates -- than milk. And while milk and yogurt have similar amounts of lactose, yogurt may be easier to tolerate because the active cultures it contains have already broken down some of the milk’s lactose during the fermentation process.

Try eliminating the most high-carb dairy from your diet, as those are more likely to be the foods that contain the most lactose. If your symptoms improve or disappear, you may not necessarily need to avoid all dairy products.

Artificial Sweeteners

Artificial sweeteners, also known as noncaloric sweeteners, are a mainstay of the average low-carb diet. Whether you use them to sweeten your coffee or to transform traditional recipes into more palatable, low-carb recipes, boosting your intake of artificial sweeteners can wreak havoc on your digestion. Sorbitol, an artificial sugar found in some low-carb food products and also used to sweeten beverages, has a laxative effect when consumed in sufficient quantities. According to the website Food Intolerance Diagnostics, healthy adults can develop diarrhea and other gastrointestinal symptoms after consuming as little as 5 grams of sorbitol, while more than 50 percent of adults experience such symptoms after consuming 10 grams of the artificial sweetener.

Mannitol and sucralose are other common artificial sweeteners that may cause gastrointestinal distress. While it may be hard to eliminate artificial sweeteners if it’s how you satisfy your sweet tooth on a low-carb diet, cutting back for a couple of weeks may help you determine if it’s what’s driving your gastrointestinal problems.

When to See Your Doctor

Your digestive system is complex because it’s influenced by a wide variety of factors apart from diet, including stress and illness. If you’re able to rule out dietary changes as the cause of your diarrhea but the problem persists, it’s a good idea to see your doctor. Having diarrhea for longer than four weeks is considered chronic, and chronic diarrhea may be a sign that you have a more serious underlying health problem.